A mechanical coolant is a coolant pump which is driven by the combustion engine, for example, by using a driving belt driving a driving wheel of the pump. As long as the combustion engine is cold, only a minimum coolant flow is needed. Mechanical coolant pumps are therefore used which are provided with an outlet valve for controlling the coolant circulation flow. As long as the combustion engine is cold, the outlet valve is closed so that the circulation of the lubricant is minimized, with the result that the combustion engine warming-up period is decreased.
Usually, outlet valves are used in the form of a pivoting flap, whereby the pivoting flap is positioned in the lubricant outlet channel. The pivoting flap can be controlled to rotate the flap into an open or closed position, whereby the positions determine the coolant circulation flow. The arrangement of such a pivoting flap inside the lubricant outlet channel, however, restrains the coolant flow even at the open position of the flap and induces a flow resistance. Such pivoting flaps can furthermore jam as a result of abrasion, distortion and particles in the lubricant which adhere at the flap and the recess for the flap.